TUESDAY, Dec. 9 (HealthDay News) -- The rate of HIV transmission in the United States has dropped 88 percent since 1984 and 33 percent since 1997, even though the number of people living with HIV in the United States has increased, researchers reported Tuesday.

The study, done by Johns Hopkins Bloomberg School of Public Health and the Centers for Disease Control and Prevention, appears online and in a future print issue of the JAIDS: Journal of Acquired Immune Deficiency Syndromes.

"For every 100 persons living with HIV today, five or fewer will transmit the virus to an uninfected person in a given year. In other words, 95 percent or more of those living with HIV do not transmit the virus to others, which indicates that prevention efforts are having a real impact," lead author David Holtgrave, chair of Bloomberg's department of health, behavior and society, said in a Hopkins news release.

The annual transmission rate in 1984 was 44 per 100 people with HIV, the virus that causes AIDS. That declined to 6.6 per 100 in the early 1990s and rose slightly in 1997 to 7.5 per 100. That was the year that new antiretroviral therapies became available, which may have led some people at risk for HIV to forego prevention measures, the researchers said.

"The declines (in HIV transmission rates) reflect the success of prevention efforts across the nation," study co-author Richard Wolitski, acting director of the CDC's division of HIV/AIDS prevention, said in the news release.

"However, despite this success, we cannot forget that new HIV infections are increasing among gay and bisexual men, and that African Americans and Hispanics continue to experience disproportionate and unacceptably high rates of HIV and AIDS. The fight against HIV is far from over," Wolitski added.

More information

The U.S. National Institute of Allergy and Infectious Diseases has more about HIV infection prevention.